Does the average person, who is not obsessive, build upon at least all acts of worship, and has a Hadith been reported with this meaning?

The basic principle is that whoever doubts the number of rak'ahs in his prayer, whether he prayed three or four, should build upon the lesser number (three); because one's obligation is not discharged except with certainty. Then, he should perform two prostrations before the salutation, due to the Prophet's (peace be upon him) saying: "If one of you doubts in his prayer and does not know how many he has prayed, whether three or four, let him cast away doubt and build upon what he is certain of."