go to someone's head
US /ɡoʊ tə ˈsʌm.wʌnz hɛd/
UK /ɡoʊ tə ˈsʌm.wʌnz hɛd/

1.
if success or praise goes to someone's head, it makes them feel more important than they really are
:
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Don't let that small victory go to your head.
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After winning the award, his ego really started to go to his head.