on earth, a substitute

I can't accept it.

私は納得できません

I can't accept it at all.

私はいったい納得できません

I still can't accept it at all.

私はいったいいまだに納得できません

I still can't accept at all what he does.

私はいったいいまだに彼が納得できません

I still can't accept at all that he does it for no reason.

私はいったいいまだに彼が理由もなく納得できません