conjecture
忖 centers on forming a tentative judgment or guess about something, especially when direct knowledge is lacking: conjecture, surmise, or estimate.
忖 combines 忄 (heart/mind) with 寸, which likely contributes a phonetic element. The character suggests measuring or gauging with the mind, fitting the idea of conjecture.
The heart radical 忄 beside 寸 (a measure) suggests the mind measuring something without full information: a conjecture.
For ソン, imagine a son guessing what his father is thinking: son -> ソン, and his mind (忄) measures (寸) the situation.