This is a basic courtesy. Avoid patronizing and paternalistic attitudes. Do not tell someone with a disability you admire their courage and strength. In the same vein, it is not necessary to feel pity for persons with disabilities. In fact most people do not particularly appreciate this type of emotional response.
Life is a challenge for all.
Many of us were raised with the principle that it was not polite to stare. Remember that, if you catch yourself staring at a person with a disability. Negative attitudes or inaccessible entrances to buildings are examples of handicaps. Persons who are not disabled are all different, and the same applies to persons with disabilities. Functional limitations or abilities will vary.