jack of all trades, master of none
A literary, somewhat self-deprecating expression for someone who has dabbled in many things but lacks deep expertise in any. The image is of a mole cricket, which can dig, swim, and fly but excels at nothing.
He is a jack of all trades and master of none; he tries his hand at many things but never fully commits to any.
From the kanji 螻蛄 (mole cricket) and 才 (talent). The mole cricket is said to have many mediocre abilities (digging, swimming, flying) but excels at none, hence the metaphorical meaning. The exact historical origin of the phrase is uncertain.