Why is happiness so difficult to achieve?  We certainly have all heard the advice: focus on the good and on the blessings you have and you will become happy.  That definitely has a profound lesson in it: we do need to focus on our blessings, to acknowledge the good, feel gratitude and be happy. But is that the entire solution?
I see so many people who do appreciate the good they have….but they cannot get past the emotional downs they experience from various problems they may have.
For example, a man may truly appreciate his wife, his children, the community he lives in….but if he has no proper parnassa, cannot pay his bills and struggles constantly to put food on the table, is it enough to tell him to be grateful for what he has? I think not. In fact, I think that is insensitive.
If a person is single and getting older and is having a very hard time finding a shidduch, will it help to tell the person just be happy about what you have and focus on that? I think not. 
Of course anyone who is able to help someone who is struggling, that is the greatest mitzvah: to try to relieve the hardships of another person is a true chesed. That is why Chassidus teaches that you cannot really help a person spiritually if you have not helped him first materially. if things are not okay with a person’s material aspect of life you cant just jump to the spiritual. You can encourage a person spiritually,but you cant only do that. You need to see what he needs materially as well and do your best to fill that lack.
But why is it that people get so depressed when they are lacking parnassa, a shidduch, children or health? Part of the reason is because people start imagining “what if”. What if they never get a good parnassa? What if that shidduch never shows up? what if they never are  blessed with children? What if their health does not improve? And those “what ifs” lead to further imagination of all sorts of negativity and make a person feel miserable in life. So it does become hard to focus on the good. A person imagines themselves remaining in a miserable state forever. 
So let’s analyze this more: perhaps the problem is that we are lacking emunah. We worry about things, which means we do not believe somehow that things will improve or we will be blessed with what we want or need. So number one: we need to strengthen our faith. We need to believe Hashem is in charge and will help us and will provide what we need. We need to really believe that with an unshakable faith.
The next thing to understand is that whatever is happening and whatever situation we are in, is because Hashem wants us to be in that situation, for whatever reason. Knowing that, we can begin to look for the good in the situation:  what we learn from the situation, what we gain out of it, what we do to inspire others because of it etc. etc.
And of course we need to believe that no matter what, our situation can improve. If we lose hope, that is where depression really starts from. In fact, most of the time depression stems from lost hope. We feel maybe such and such will never happen, maybe such and such will take forever, maybe things wont get better etc. etc. That negative mind set is what gets depression going. So, although it is difficult at times, we need to learn to think positively. 
Another major problem is when we compare to what we had and to what our situation is now. If a person used to live by the beach and now moved to a regular city with no beach around, one may compare and say “Oy, I miss the beach.” Being dissatisfied with one’s situation will lead to depression for sure. If one used to be wealthy and then fell on hard times and is living from pay check to pay check, definitely one will compare situations. What helps is to realize this is just  a test from Hashem: will your happiness  be based on serving Hashem or on having what you think you need? And can you make yourself happy with your present situation and not feel you are lacking something? Can you learn to appreciate what you have now without comparing to what you had before? Can you realize that this is all what Hashem wants and therefore accept it with joy?  It requires work. It requires conscious effort to establish new thinking patterns but it can be done.
Also when a person has any sort of difficulty or problem in life, it is helpful to understand that perhaps things could have been far worse. This is really a kindness from Hashem which we cannot fully comprehend but to realize it could have been worse, keeps us in perspective and helps us to appreciate and thank Hashem even for those difficult times.
Sometimes people have certain problem and start feeling sorry for themselves, wishing things were the way they used to be or that they could have things the way their friend has it (we compare far too much to others)……until they hear of someone else who had the same problem and things turned out even worse. Then they are able to become grateful for what they have and be thankful for that. It is all about perspective.  comparison is only good if you compare to someone who has it worse, not someone who has it better. 
If you internalize all these messages, you will begin to feel happier. Happiness is something you have to DO. You cant wait to feel happy. It may not happen. You need to BECOME happy. You need to consciously change your mind set. You need to focus on the good you have, and not compare to others or to what you had before. Just learn to be thankful for each day and to appreciate anew what G-d is giving you  now. To really trust that He will provide all your needs even if you feel you are lacking something. Then you learn to be grateful for everything and to become happy with your present situation . Living in the past is not beneficial at all. Look forward to a happier future!