This is probably the single biggest grammar habit to build as a Thai speaker, so slow down here. In Thai, a verb NEVER changes form no matter who is doing the action: 'ฉันกิน' (I eat), 'เขากิน' (he eats) — 'กิน' stays exactly the same. English verbs are different: when the subject is he, she, or it (a single person, animal, or thing — not 'I', not 'you', not plural), the verb in the present simple gets an extra '-s'.

Compare: 'I work' / 'You work' / 'We work' / 'They work' — no change. But 'He works.' 'She works.' 'It works.' This one letter is easy to forget because Thai has nothing like it, so it needs deliberate, repeated practice, not just understanding the rule once. 🔊