When it comes to disability, looks can be very deceiving.  There are many people who look quite healthy but who are quite disabled by anyone’s standard.  For instance, many individuals who suffer from very severe psychiatric illness are physically healthy and able to do things such as mow their yards.  Some people function quite well at times especially around their own homes.  At other times and under other circumstances or in different environments, they cannot function well enough to perform a job on a sustained basis.  You simply may not see these individuals when they are at their worst.