Proper surface preparations is key to a successful project. Coatings require a cleaning to ensure surface is free of dirt, dust, grease mildew or mil glaze. Briskly sand all surfaces with a 60-80 grit sandpaper or chemically clean & brighten with a biodegradable solution.
When doing a new wood surface, clean before you sand! Even new wood needs to have these steps taken to ensure success! New wood develops a coating called "Mil Glaze", if this coating is not sanded off, your stain will not penetrate.
If you are re-coating an existing finish, the surface still needs to be cleaned with a Wood Cleaner prior to new coat of stain.
Never coat wet wood! If moisture is visible, or it has rained or been recently washed, the wood is too wet to stain. Allow surface to dry for 48 hours.
Never apply stain in direct sunlight. If it is warmer than 25°C, or your surface is hot to the touch, hot temperatures force stains and coating to dry before they penetrate.. we call this "Flash Drying". When this occurs this will cause the coating to fail and peel.
Do not over apply! Applying excess film thickness will limit the coatings ability to breath in which will cause it to fail.
"High quality wood stain does not fail"
Regardless of the product that is used, if steps of preparation are not taken, proper application methods are not used and or temperature is not sufficient. Anything will fail.
"Staining with a roller is faster"
Very true, however the BEST application method to ensure the stain does indeed penetrate into the wood grain can only be done with a brush. This could make or break your staining project.