Prosecutors don't charge people if they aren't fairly confident that the evidence will result in a conviction. However they will also be willing to bargain for a plea to save the effort and expense of a trial. This lets them get more cases through the system in less time. They (or the police) might also try to pressure a suspect to confess, just to see if he will. That saves them even more time.

So bottom line, you should never admit or confess to anything. If the prosecutor has enough evidence, he'll probably start with an offer of a plea deal. If his evidence is marginal, he might try to get a plea but likely won't bring charges if he thinks his chances in court are iffy.

If you go to trial anyway, in the face of strong evidence against you, then you've probably lost your chance at a light sentence, modulo how good a defense you can afford.