Why Is Early Exercise of a Call Option on a Non-Dividend-Paying Asset Generally Suboptimal?

Early exercise of a call option on a non-dividend-paying asset is suboptimal because the holder gives up the remaining time value (extrinsic value) of the option. The option is always worth at least its intrinsic value, but holding it allows the possibility of a greater gain if the underlying price increases further.

By exercising, the holder also forfeits the interest that could have been earned on the strike price until the expiration date.