Explain how Mendel was able to disprove what most people during his time believed about inheritance

The famous Mendel's pea plant trials proved that at least two types of alleles, dominant and recessive. must exist. Say eg a red plant, homozygous dominant, RR is crossed with a white plant, homozygous recessive, rr. Earlier people thought that all the new bred plants will be pink but Mendel found that they were red instead. The reason was that all of the springs were heterozygous, means each one had one dominant allele, Rr, and one recessive allele, rr. When this happens, the dominant form of trait exhibits in the next generation, in our case red.