ignorant of, misgivings, interrupt, stop
懝 centers on a mental state of being blocked or unclear: ignorance, doubt, or interruption. The meanings 'ignorant of', 'misgivings', 'interrupt', and 'stop' all describe a mind that is halted or unable to proceed smoothly.
懝 combines 忄 (heart/mind) with 疑 (doubt), suggesting a mind filled with doubt or uncertainty. The exact historical development is uncertain, but the phono-semantic structure is plausible.
The heart radical 忄 beside 疑 (doubt) shows a mind stuck in hesitation. When your heart is full of doubt, you become ignorant of the truth, have misgivings, and your thoughts are interrupted or stopped.
For ガイ, imagine a guy who is always doubtful and interrupts conversations with his misgivings: guy -> ガイ, and his heart 忄 is full of 疑.