The Hattrick community is colourful, it really helps expand the Hattrick world. You can find plenty of helpful managers that can help you with Hattrick and real life questions.
I was ranked 1st of all teams in Botswana after the first league round, that was one of the best achievements for me in Hattrick. Of course there's a lot of luck involved there, but hey, they're never going to be able to take that away!
One reason I play Hattrick is because I like the cyclical nature of the game. You start with an idea about what kind of team you want to build, then you train long-term (up to 3 years in real life!). While you build, you can test and try to comprehend the aspect of the match simulation that you want to master. I also like the tactical choices you have to make for each match. But the most important component is the community.
What I like about the Hattrick community is that there are real people and you don't just compete against the computers. You play against each other, but you can also help each other in the forum and talk about everything.
My best Hattrick memory was when the city where I lived (L'Aquila, Italy) was hit by an earthquake. I received a lot of support, a lot of help, a lot of love. It was a very hard time and Hattrick was there, with its community, with me. I will never forget that.
I would say the community is the strongest reason I have stayed in Hattrick for so long. The game too of course. After having trained my players and played in the French Division 2 for a while, I started focusing on training international players to help the Moroccan team. Today 80% of the defense of the Atlas Lions was trained by me!