Using a mechanical switch or touching wires together to change from 0 to 1 or 1 to 0 is not reliable for sequential logic circuits. The connection between the contacts or wires will have some "bounce," meaning that electrical contact between the wires is not solid. This produces several transitions rather than one. Counting circuits will count all of the transitions rather than the single switching event. A debouncing circuit could be used to eliminate the effects of contact bounce.
This is an oscilloscope trace showing contact bounce. Two wires were touched together to go from 0 to 1. Note the
numerous transitions actually present in the signal.