The general summary below might be helpful. Even though the examples all use says or said, the concept applies to other verbs. The problem with "I thought" is that it is often used to mean "I used to think" and to introduce a subsequent contrast:
I thought I was stronger, but now recognize that I'm not.
It's harder to come up with an "ongoing-truth exception" using "I thought". The examples in #2 aren't convincing.
The term “sequence of tenses” refers to the relationship of tenses in subordinate clauses to those in principal clauses. Generally, the former follow from the latter.
(1) When the principal clause has a verb in the present (“he says”), present perfect (“he has said”), or future (“he will say”), the subordinate clause has a present-tense verb. Grammarians call this the primary sequence.
(2) When the principal clause is in past tense (“he said,” “he was saying”) or past perfect (“he had said”), the subordinate clause has a past-tense verb. Grammarians call this the secondary sequence.
(3) When a subordinate clause states an ongoing or general truth, it should be in the present tense regardless of the tense in the principal clause — thus “He said yesterday that he is Danish,” not *”He said yesterday that he was Danish.” This might be called the “ongoing-truth exception.”
*Invariably inferior form.