As someone mentioned already the required bankroll will tend to increase with the size of the tournament. 100 buyins is enough for smaller tournaments, but if you always play tournaments with 1.000 or even more participants, its not enough.
The reason is, that even in such large fields, a big chunk of the price money goes to the top. The winner alone might take 20% or 200 buyins, so its common sense, that you will be trailing behind your long term results, until you actually win one, and that this can be for a very significant amount of money and last for very many tournaments.
If however you only play large tournaments now and then, and your daily grind is in cash games, SnGs or small tournaments, then this does not really matter, because you will have a way to win back that money, you might lose on the big tournaments, until you take on of them down. Then you can see the entry to the big tournament as a kind of lottery ticket, and if you fail to win in the lottery this time, its no big deal.
Some tournaments are actually so large, that you will never get past variance. The Sunday Million for instance is now a 10.000+ player affair, which mean, that even if you play it every weak, you can not expect to reach the final table more than one time every 20 years.