I think most of the time, good, really good lessons are learned the hard way. Such as me leaving my paint box palette filled with paint to harden ... for one week.
See the dried up mess on my almost new Guerrilla paintbox palette below? Ouch, what a mess.
Next photo you see a paper towel with paint scrapings from the above palette. I ended up using a palette knife, odorless turp and a retractable razor trying to remove the dried on paint. Some big globs, some small smearings of paint. All very hard to remove from the wood palette.
After working on this for quite awhile I've finally removed all the paint and I've learned my lesson to never leave the paint on my palette this long again.
In Kathleen Dunphy's workshop her palette was a beautiful grey that had accumulated from wiping up the oils. After time it had turned a beautiful hard smooth surface. I think I'll try this next time before my paint dries too hard. I chalk it up to being new at oils, what do you think? Have any of you learned this lesson the hard way?