Why did the two roads appear similar to the poet?

I believe you are referring to "The Road Not Taken" by Robert Frost. As the poem begins, the poet is poised between two roads in the woods, and they at first look similar enough to the poet to both be appealing. He looks down the first road to the point at which it bends out of sight. He then looks at the second road, which looks grassy and untrod, as it "wanted wear."
However, at the point where the poet stands, "the passing there/Had worn them really about the same." In other words, at the point where the poet stands, there is a lot of foot traffic that has worn down both paths to the same degree. In addition, "And both that morning equally lay/In leaves no step had trodden black." That means that both paths presented the same amount of leaves that have not been stepped on. However, as the poet takes the second path, he says, "I took the one less traveled by." He realizes that this path is less trod on as he follows it further, and it has "made all the difference," meaning that taking this less used path has forever affected his future.