Why Is Early Exercise of an American Call Option on a Non-Dividend-Paying Stock Generally Not Optimal?

Exercising an American Call option early on a non-dividend-paying stock is generally not optimal because the holder sacrifices the remaining time value of the option. By exercising, the holder gains the underlying asset but loses the option's embedded insurance against a price drop and the leverage provided by the option.

It is better to sell the option or hold it until expiration.