There is a great deal of mystery and myth for many student pilots surrounding the first solo flight. This has resulted a number of common misconceptions which sometimes creates unnecessary stress for the student, especially if left unaddressed by the instructor. The simplest way to put these misconceptions to rest is to have a look at the Federal Air Regulations, where the requirements for solo flight are spelled out.
According to the FAR, in order to solo, there are two basic requirements: The student must first have a Student Pilot Certificate, which is normally issued by an FAA Medical Examiner together with a Third Class Medical Certificate. While a student pilot may begin his training prior to obtaining this certificate, he/she must have it before the first solo flight. The second requirement is that the student's instructor must authorize solo flight by making an endorsement in the student's logbook. There are a number of guidelines set forth to help the instructor evaluate a student's readiness to solo, including knowledge requirements (which may be tested orally or by a written test), and the demonstrated ability to perform certain maneuvers, but in the end the determination rests with the instructor.
Thus, the decision is a subjective one, and there is no set number of flight hours which define when a student is ready. This is the point which often confuses and frustrates student pilots. At some point along the way, students will get it into their heads that if they do not solo by X number of hours, that it means that they are not good pilots. While some student pilots may chide each other in this regard, it has very little real significance. After the student earns his license, he will likely never think of it again. After all, when a prospective pilot is interviewed for a job by an airline, the number of hours he required to solo is not a serious consideration. They are a lot more interested in how many hours he has now, and what his overall performance record is like.