The piano is terrific to learn because it lends itself well to so many different occasions. It's a lovely solo instrument, and it collaborates well with other instruments. A student has the added benefit of learning to read both bass clef and treble clef while learning the piano, unlike most instrumentalists who just learn a single clef. The visual layout of the keyboard helps students instinctively grasp concepts of music theory, with its whole steps and half steps laid out all in a neat little row. Unlike many instruments where a student has to struggle to achieve the desired sound, a piano has an appealing tone just by merely pressing a key, which helps a student feel successful in her musical pursuits almost right away!
Things can get tricky when a student starts playing multiple notes at a time with challenging rhythms. This is often where bad habits start to appear. Instead of learning the "right way" to do things, many students learn the "good enough" way to do things, which will hamper their musical development. Their fingers will trip over each other on the keyboard, with rhythmic idiosyncrasies, poor phrasing, and posture problems. Even in these days of You-Tube videos designed for self-directed learners, EVERYONE DEVELOPS BAD HABITS, and there's just no way of knowing what you might be doing wrong unless you collaborate with someone trained to identify these common trouble spots.