Don't run away with more than you can carry.

The image is of someone trying to get away with so much that the weight itself makes escape difficult. Taking more can become a disadvantage rather than a gain.

The broader warning is to keep what you take or undertake within your capacity. An excess that looks attractive at first may leave you unable to make good use of it.

Use this as a warning when someone is tempted to take on too much or claim more than they can practically handle. It emphasizes the trouble caused by excess, rather than praising restraint for its own sake.