5週1日目 信じがたい
Evaluation・cause・basis
接続：V-stem＋がたい
psychologically or intrinsically difficult
注意 / Note：がたい tends to be difficult to accept in terms of psychology and writing; にくい is difficult to be objective; づらい is difficult because of emotions or situations.
比較 / Compare：Same song: 〜にくい／〜づらい. These models are often mistakenly chosen for each other — carefully read the 接続 and nuances above and then decide.
よく出る形 / Common form：動ます形＋がたい。The reason is PSYCHOLOGICAL or the nature of the thing, not technical. The number of verbs that can be used is small: 理解・想像・信じ・忘れ・許し・受け入れ.
彼の行動は理解しがたい。
Their actions are difficult to understand.
忘れがたい経験になった。
It was an unforgettable experience.
あの日の光景は今も忘れがたい。
The scene that day is still unforgettable.