To clamber is to climb awkwardly. Hamlet's Ophelia was said to have been clambering on a weak branch of a willow when she met her "muddy death." It's never a good idea to clamber, let alone on weak willow branches.
We associate the word clamber far more often with toddlers (than Shakespearean tragedy). Toddlers are known for naturally clumsy, ill-coordinated movements we deem cute not foolish. Suitably enough, the word comes from the delightful and long obsolete Middle English word clamb, meaning the past tense of climb, a word that has all the happy logic of a toddler's imagination.