The Bonferroni procedure performs a number of pair-wise comparisons with t-tests and then multiplies each p-value by the number of comparisons made. This ensures that the probability of making any false rejection among all comparisons made is no greater than the chosen significance level α.
As a consequence, the higher the number of pair-wise comparisons you make, the more difficult it will be to show statistical significance for each test. But the chance of committing a type I error also increases with the number of tests made. The Bonferroni procedure lowers the working significance level of each test to compensate for the increased chance of type I errors among all tests performed.