Obligation & Inevitability: ざるを得ない vs ないわけにはいかない vs べきだ
English collapses this cluster into "have to / should / can't help but". Japanese splits it by the *source* of the pressure: outside circumstances, personal principle, general truth, subjective judgement, or uncontrollable emotion.
The patterns
ざるを得ない
have no choice but to (forced by circumstances)
台風のため、イベントを中止せざるを得ない。
Because of the typhoon, we have no choice but to cancel the event.
ないわけにはいかない
can't not do it (duty / principle won't allow it)
招待された以上、出席しないわけにはいかない。
Since I was invited, I can hardly not attend.
ものだ
it is the nature of things that; one naturally does
年を取れば、体力は落ちるものだ。
As you age, your stamina naturally declines.
べきだ
should; ought to (speaker's judgement of what is right)
約束は守るべきだ。
You should keep your promises.
ずにはいられない
can't help doing (impulse you can't suppress)
あの映画を見ると、泣かずにはいられない。
When I watch that film I can't help crying.
てしかたがない／てたまらない
unbearably ~ (intensity of a feeling)
会いたくてたまらない。
I miss them terribly.
Decision procedure
Is it an uncontrollable feeling, or a rational judgement / rule?
Is this about one specific situation, or a general truth?
Where does the pressure come from?
Commonly confused
ざるを得ない vs ないわけにはいかない
Both translate as "have to", but the first is forced from outside and the second is held from inside. Test: remove the external pressure and ask "do you still have to?" — if yes, it is ないわけにはいかない.