...and I could have done this, too, if things had been different. (Para. 11)
Meaning: I could have done this, too, if I had not been severely crippled like this.
In this sentence, the if-clause expresses a condition just the opposite of the real situation. Please watch the use of the past perfect tense in the sentence. More examples are:
If he had studied hard last term, he would not have failed in the final test. 要是上學期努力, 那大考他就不會不及格了。
If I had taken the doctor's advice and rested for a few days, I should have completely recovered by now. 要是我聽醫生勸告, 休息幾天, 我現在該完全恢復了。