Simplify the following text for a Grade 8 native English-speaking person.
Original: Horowitz stopped playing concerts four times ( 1936 to 1938 , 1953 to 1965 , 1969 to 1974 , and 1983 to 1985 ) , as he was unsure that he was good enough , even when he was popular .
Simplified: Several times , he withdrew from public performances - during 1936 to 1938 , 1953 to 1965 , 1969 to 1974 , and 1983 to 1985 .