Politically speaking, a deputy president should not be seen acting as 'president in waiting' or 'an alternative president'. They must be presidential material but 'paying all tribute' to the head of state.
The first DP, Dr William Ruto, exposed some weaknesses in the presidency as encapsulated in our Constitution. Being over ambitious and wanting to be President, he had a chance to define, to other DPs, the "how" to deputise. More importantly, he defined, knowingly or unconsciously, the "when" a deputy president should stick his head out.