How to beat computer ?

I was wondering how can a human player beat a computer player. Take rybka for instance, with such a capacity of calculating. It can analyse all good and best moves. Then it will play all best moves. When computer will be playing all good moves then how can a human player expect to beat a strong engines or chessmaster or fritz. I know great grandmaster beats even such machine. So my dilemma increases. When a rybka can move all good moves then how a grandmaster beat such machine? First i thought that human players can't beat rybka or strong engines since they can make strong and best moves but when i made little research i realize that there are grandmasters who actually beat such engines. So now i wonder how they do it ? 

Does my assumption that engines can make always best move is wrong? 

We can't be sure whether engines always make the best move, as there is no way to find the best move in a given position (except for forced moves) at the moment.

Also note that noone has beaten Rykba without odds for a long time, possibly ever,

but they can make long calculation. It helps to identify best move. 

Yes that's wrong, but the comp's finds really good moves, but sometimes they need help from human's to find the right plan.

Take a look at CC, (postal chess, human and computer working together)

Who will win in the following position, or is it a draw?

Did you consider all possible moves that each player can play, before figuring out who wins or whether it's a draw? How many moves did you calculate ahead before coming to a conclusion? My chess engine was considering all possible moves, and calculated more than 15 moves ahead, still considering black to be ahead by about 6 points.

If you can figure out the result of this position some other way than simply considering all possible lines (except for the lines which result in losing a queen or rook without compensation), then you can do something that the computer (my chess engine, at least) isn't (yet) programmed to do, which gives you a (possibly tiny) advantage over the computer. The computer has the (possibly big) advantage of speed and precision, though.

Grandmasters can do something (not sure exactly what or how, though) that the computer isn't (yet) programmed to do.

it's look too difficult question .!!but the human can beat the computer coz the human made it : -)

I would also really like to know what the weaknesses of a computer are. I would suppose it would be the positional understanding more than its strategic understanding, as computers can of course calculate very precisely, but it could be fun to hear something from people with experience in this matter.

BTW, Cyp - That was one thilling game you showed us there! "Threatening to threaten the c4 pawn.!!". "A subtle move, the queen is safer there." LOL!

i had defeated the computer at easy stage..very funny, only one king is left to him

 That's as wrong as suggesting that humans can run faster than a car because we built cars.

 The weaknesses are strategy (positional understanding), the ultimate strength is tactics.

I'd challenge anyone who suggests that the human world champion would be able to beat the computer world champion (the same configuration that won the computer world championship, not a weakened machine running on a mobile phone). I guarantee that the computer would crush the human and for the human a successful game would be a draw.

A

draw, but without the rook it is a win, as black can sacrifice his/her queen for a whit pawn.