To overreach means to try to do more than you're actually able to do, or to extend yourself beyond what's reasonable or wise. When someone overreaches, they're reaching too far, like stretching your arm to grab something on a high shelf that's just out of range: you might knock things over or lose your balance in the attempt.

A student overreaches when she signs up for five difficult clubs, two sports teams, and advanced classes all at once, leaving herself exhausted and unable to do any of them well. A company overreaches when it tries to expand too quickly, opening dozens of new stores before it has enough money or staff to run them properly. A chess player overreaches by launching an aggressive attack before her pieces are properly positioned, leaving her king vulnerable.

The word carries a sense of ambition gone too far. There's nothing wrong with being ambitious or trying hard things, but overreaching means misjudging your own limits or resources. When people overreach, they often end up in a worse position than if they'd been more careful. A basketball player who overreaches trying to steal the ball might foul out of the game.

You might hear someone warn, “don't overreach yourself,” as advice to be realistic about what you can handle. The key is finding the balance between challenging yourself and attempting something genuinely beyond your current abilities.