Tolerance Principle: because I believe input design should be flexible and tolerant, preventing chances of errors by all means and presenting a user friendly interface.
YES I Agree "Garbage in Garbage out"
To reduce the likelihood of "Garbage going in to a system, a designer should implement checks and validation mechanisms. Check mechanism are procedures which examine data supplied and determine whether its of the desired format. Validation Mechanism are procedures which check the validity of the data by examining what a user has supplied against a predefined data.
For example a user can supply a date of birth as 12/12/1890. We know well this person must have died, Now according to the check mechanism the data is a date but its not a valid date of birth for a living person.