When you put it this way, it does sound kind of ridiculous, doesn't it? IMHO, it is not the universe which is providing the happiness or unhappiness. Rather, it is our own perception of what the universe is providing based on our own positive or negative mindset. When we have a positive state of mind, we are more likely to see the gifts, options, and opportunities that surround us. When we are in a negative mindset, we tend to be blind to all the good stuff.
I don't believe self-esteem is the only reason, but I do think it is a major player. It goes back to what Falcor mentioned, about needing action in addition to thought. I think people with low self-esteem are less likely to take the necessary actions to get themselves out of whatever rut they are in.
I am guilty of reading "The Secret", so I have tried this technique. Specifically, I was looking for a new rental property for my massage business, and there was a particular office in town that always attracted me. It was the perfect location, perfect size, perfect everything, and I began visualizing myself as the renter of that property. Random coincidence? Not sure. I will say that I did take the necessary actions in addition to the thoughts, checking often with realtors/websites/rental listings. In any case, I am now the proud renter of that lovely office.
It is funny.
I can see low self-esteem might prevent someone from taking action which is an important part. The danger I find with some of these spiritual ideals and labels is that they can seem judgmental and counterproductive if one truly is on a path of spiritual development. Attitudes like, "So and so is in lack. Stay away from So and so because they will bring you down..."
That sounds good about your workspace, but was it really law of attraction or just making something you want happen?