Poker can be a very, very streaky game and no-limit is no exception. However, unlike the long steaks of dead cards that can weaken a limit players bankroll, a no-limit player can expect to win four out of five sessions. It isn't the bad cards that will ruin him... it will be over-reaching to bigger games, losing focus, and going on tilt.
A no-limit player can lose his entire bankroll in a single night if he isn't careful, something that a no-limit player rarely has to consider.
I generally advise that a no-limit player have at least forty buy-ins to the game he intends to play.