How did Mendel explain that it is possible that a trait is inherited but not expressed in an organism?

When Mendel crossed pure tall (TT) pea plants with a pure dwarf (tt) pea plants, in the F1 generation he found that all pea plants were tall (Tt). There were no dwarf plants produced in an F1 generation. When he self-pollinated these Fl plants, in the F2 generation he obtained tall and dwarf plants in the ratio 3:1.

Thus as three-fourths of the plant in an F2 generation are tall and one-fourth is dwarf so tall is a dominant trait whereas dwarf is a recessive trait which expressed itself only in homozygous condition. The dwarf trait was inherited in an F1 generation but it does not get expressed, it remains suppressed in presence of dominant trait tall.

Reappearance of the dwarf pea plants in F2 generation proves that the dwarf trait was inherited but not expressed in F1 generation.

A character is expresses depending upon whether it is dominant or recessive. A trait which is inherited, if it is a dominant character, then it will be expressed. While a trait which is a recessive character will not be expressed.