Mendel's success can be attributed to several factors, but the most important one is his approach to studying the inheritance of traits. He considered one character at a time, which allowed him to make clear and precise observations and draw accurate conclusions. This method is known as the monohybrid cross.

Here are some of the key reasons why focusing on one trait at a time contributed to Mendel's success:

1. Clear and precise observations: By looking at only one trait, Mendel was able to make clear and precise observations about how it was inherited. He could easily track the trait from one generation to the next, which helped him to identify patterns and make accurate predictions.

2. Elimination of confounding variables: Focusing on one trait at a time allowed Mendel to eliminate the influence of other traits that could have confounded his results. This made it easier for him to identify the underlying principles of inheritance.

3. Development of clear theories: By studying one trait in isolation, Mendel was able to develop clear and concise theories about how traits are inherited. He could identify the factors that controlled the inheritance of that trait and make predictions about how it would be passed on to future generations.

4. Replication of experiments: By focusing on one trait at a time, Mendel was able to replicate his experiments multiple times to confirm his findings. This gave him confidence in his results and helped him develop a robust theory of inheritance.

In summary, Mendel's success can be attributed to his methodical approach to studying inheritance, which involved focusing on one trait at a time. This approach allowed him to make clear and precise observations, eliminate confounding variables, develop clear theories, and replicate his experiments to confirm his findings.