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Sequence of Tenses.
In a complex sentence :-
1. If the principal clause is in the past tense, the subordinate clause must also be in the same
Exceptions:
i) When a comparison is being made using the conjunction 'than' or 'as well as'.
ii) When a universal truth or a habitual action is being talked about.
iii) The things being talked about are still relevant at the time of speaking.
2. If the principal clause is in the present or the future tense, the subordinate clause can be in any tense.
3. In the case of some purpose being discussed - 'may' Is used with the present or the future tense , and 'might' with the past.

('in this video, 'could' in the main clause is in the past tense, hence use 'was' in the subordinate clause and not 'am'.)