Someone with high functioning anxiety will usually look like they are confident and successful to the outside world. Close friends may be aware but most are able to hide their anxiety well and it usually propels them to work harder and be outwardly successful.
The following are just some of the positives the others see:
Appears outwardly calm and collected
And here are just some of the negatives that are not always obvious to others:
Need for reassurance
Rumination dwelling on the negative and past mistakes
Inability to say "No
Feeling intimidated by the future
The tendency to compare yourself to others
Potential for unhealthy coping methods e.g alcohol etc.