1) Patience - sometimes the best things in life come to those who wait. We are reminded of that every year in baseball as guys who had little impact in the first half of the season go on a tear in August and September and lead fantasy teams to titles. Things have a magical way of finding their level in baseball. Those guys may not even be on a roster right now.
2) Persistence - Have a team that's struggling? Sitting in the basement in your league? Keep grinding. The race is long. Just like the stories of the guy who worked his way from mopping floors to sitting in the corner office, we have the tales of teams seemingly buried in May who take home cash in October.
3) Humility - They say that everyone in baseball gets humbled by the game at some point. That is true of the fantasy game as well. Baseball is a game of failure. Fantasy baseball is a game of failure. There are no experts. Repeat, there are no experts. If you can't handle failure, don't play fantasy baseball.
4) Decision-making - Nothing says "thinking on your feet" like a live draft. It's where preparation meets chaos. Fantasy baseball is really 6 months of decision-making. Really it's year-round I guess, as you are always forming/changing opinions on players, and that impacts future decisions. In fantasy baseball you learn to make the best decisions possible, often with incomplete information. You learn when it's appropriate to take risks, and when to play it safe.
5) Acceptance - Life is full of things we cannot control. In fantasy baseball, good decisions and hard work can be un-done by a pulled hamstring or a broken hamate bone. Or a clueless manager. In life, bad things sometimes happen to good people. And in fantasy baseball, bad things often happen to good teams. Some can be overcome, some can't. But you go on.
6) Finding balance - Life is full of trade-offs. We only have 24 hours in one day. There are only 23 starting spots on a fantasy team. You can't have everything. Like in life, the key is finding balance. Homers, steals, strikeouts, saves. All the ingredients have to blended together just right to produce the perfect cake. Too much of one thing and not enough of the other leaves one feeling empty in October.