Poker is uncertain in the future?

i mean, many players who made a big winning suffer a defeat.

"isildur1" who earned 5.5M in highstakes cash game.

but he lose 8.5M and now his highstakes result is about -3M

And One of the best player in the world Phil ivey. He was a biggest winner in highstakes game.

But Since 2012, he lose 4.5M (Fulltilt ID "polarizing")

These guys are difinately best players who have high level skill.

But as time goes on, they are losing.

So i think that if you are good player, there is no guarantee of success.

what do you think about this?

If these players palyed in middle stake not highstake in which there are a lot of same good player.

Will they always succeed?