It almost always takes at least two coats of any finish to develop the sheen a finish is designed to produce: gloss, satin, flat, or whatever. The first coat seals the wood. The second coat develops the sheen.
The exception to the two-coat rule would be if you apply the first coat really thick. This can usually be done only on horizontal surfaces.
The reason two coats are usually necessary is that a lot of the first coat soaks into the wood, so there isn’t enough build to produce the sheen. If you’re applying highly thinned coats, as shown with wiping varnish in the accompanying picture, achieving the sheen may require even more coats.
It’s also almost always best to sand the first coat to make it smooth before applying the second. If you leave the first coat rough, the roughness may telegraph through and still prevent the second coat from reaching the desired sheen.