Nobody takes your shares. You keep exactly the number you had — the denominator grows. Issue new shares to an investor or into an option pool and the total outstanding rises, so every existing holder's percentage falls proportionally. Dilution is therefore not theft or failure; it is the mechanical cost of bringing in money or people in exchange for ownership.
The founder question is never "how do I avoid dilution" but "is the slice I'm giving up smaller than the growth it buys." Ten percent of a business worth $10,000,000 beats forty percent of one worth $800,000. Where founders get hurt is unpriced dilution: advisor grants handed out casually, an option pool expanded at an investor's request just before a round so existing holders absorb it, or several SAFEs converting at once. Model each event on the cap table before you agree to it, and keep the running total of what you have promised.
A concrete example: you own 100% of a business at 8,000,000 shares. You issue 1,000,000 to an investor and 1,000,000 into an option pool. You still hold 8,000,000 shares, but of 10,000,000 outstanding — 80%. A later round issues another 2,500,000, taking the total to 12,500,000 and your stake to 64%. Two rounds, a third of the company gone, and not a single share left your name.