Our earliest conscious memories seldom predate our third birthday. This best illustrates

Infantile amnesia

Explanation:

Earliest conscious memory refers to a fragment of something that happened in early childhood.

Infantile amnesia is the failure of adults to recover episodic memories, that is situations or incidents memories before the age of two or four. Infantile amnesia is caused by repression of traumatic memories occurring in the child's early psychosexual development.