You need solid dedication, a touch of insanity and a whiff of luck to become successful in Hattrick. Oh, and a feeling for mathematics.
To reach the top 100 in your league is nice of course, but it is not a real success in my eyes. I think training a talented youth player and seeing him reach the national team is a real success. Or, to help somebody else or to encourage a lot of managers to support our region's team in a Friendly Tournament! Those successes are reachable to anybody, not just the most talented managers :)
I am one of the old users who likes to do my own research to learn how the game works. I like that this is a thing in Hattrick. Not everything should be mentioned in the rules. I also like the federations where you can have some real tight friendships. More than some friends call Hattrick a forum, with a soccer-game attached to it.
My biggest achievement in Hattrick so far is that I have won some titles with my second team in Bahrain and reached the semifinals of the National Cup in Italy, but I hope, a few months from now, that it will be winning the World Cup for the Italian NT.
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!
I started playing Hattrick in the summer of 2002 when a friend, who I played "Fantasy Wrestling" with online, told me about Hattrick. I made many mistakes in the beginning. At that time there was no such thing as mentors or beginners' guides. So my very first club was bankrupt after only a few weeks. Luckily, I was able to restart with a new club shortly after that and then I did a lot better.