A go-around is a routine maneuver that is practiced at every training cycle and it isn't unusual to fly them on the line. They shouldn't be frightening to the passengers; only, perhaps, an annoyance.

Go-arounds, at least in Boeing airplanes, are not full power. The Boeing go-around power setting targets a 2000fpm climb which is less than the initial climb after takeoff. I would think that Airbus is similar but don't have never flown an Airbus.

The reasons for a go-around are usually one of the following:

1. Previous aircraft will not be clear of the runway prior to the arriving aircraft reaching the runway threshold. During in busy arrival pushes it isn't uncommon for the time between the previous aircraft clearing the runway and arriving aircraft reaching the runway threshold to be as little as ten seconds. The two airplanes are still more than a mile apart, at this point, so there is no risk of collision but it doesn't take much to eat up that ten second pad which will cause the arrival to have to go around.

2. Failure to meet stabilized approach criteria by the reject gate. Specific details vary by airline but there will be an established 'reject gate' which may be 500', 1000', etc. where the company procedures require the aircraft to be fully configured (gear/flaps), on-speed, engines spooled, on course, and with a descent rate under 1200fpm (sometimes 1000fpm). If you haven't yet met stabilized approach criteria at the reject gate then a go-around is mandatory. This usually results from ATC keeping you high, or turning you in tighter than you were expecting.

3. Low visibility. When the required visual references are not in sight at the applicable decision altitude or missed approach point a go-around is mandatory.

4. High winds/turbulence. When high winds/turbulence prevent a stabilized round-out, flare, and touchdown, result in a bounced landing, or extends the flare so that touchdown will not be within the designated touchdown zone, a go-around is prudent.