The wobble hypothesis states that there is increased flexibility in base pairing at the third nucleotide of some codons. Why does this not lead to frequent mistakes in the assembly of proteins?

This does not lead to frequent mistakes because mutations in the third nucleotide of a codon may not affect the binding of the proper tRNA anticodon. If there is an error in transcribing the third nucleotide in a codon, in most cases it will not affect the protein being produced.