Harmonica is tougher to learn then most people are led to believe - Randomly breathing in and out is easy for everyone. Going beyond that is where it starts to get harder. Most beginners have trouble learning to play harmonica with clean single notes, bending, correct breathing, jamming blues, etc. without some personalized help and feedback. For most, it's difficult to improve if you're not sure what's wrong or where to begin to fix it -- or, maybe you need some suggestions on what to practice or work on next.
Text instruction is good for learning to play. Photos and diagrams add additional information for greater understanding. Video and websites are wonderful with the multi-media effect of live-action video, text, pictures, and audio (see HarmonicaLessons.com for all these plus live online classes). Unfortunately, no matter how many books you read or videos you watch, you won't know if you are on the right track without personalized feedback.
1-on-1 Private Lessons and live online classes are unbeatable with real-time feedback for what is working correctly and for learning what needs improvement -- your questions are answered in real-time without searching all over the Internet. You will learn much faster with a 35-year teaching pro like Dave Gage who can listen and confirm instantly whether or not you are on the right track with your basic playing techniques, timing, songs, riffs, etc.