Streaks are there before you start sanding and show up when the areas around them are sanded down and the "Streakes" are not. They are mostly tool marks or end grain or figured areas that were not cut cleanly and the fibers are smashed or torn not cut. Maple is one of the worst for this to show up on as it is hard and can have lots of figure and and swirling grain. If you start out with say 80 grit, blow the dust off and go up to 120 grit you will see the streaks and then you can go back and concentrate on those areas to remove them with the larger grit papers. If you are not sure if they are gone put a little laquer thinner or naptha or DNA on the areas and they will show up and then you can keep working them out before you go through all the grits and they are still there. If the streaks are deeper, heavier or what ever than the largest grit you start with and you don't remove them the proceeding smaller grits will not take the streaks away as each successive smaller grit will remove the sanding marks of the grit before it, but not the ones that are left from other heavier grits. This is why it is important to make sure that all the sanding dust and any loose grit is removed with air before the next grit is started. You all know what happens when a stray course grit gets on the final sanding and you see all these little white swirls that really tick you off!
So cleaner cuts and proper tool control or extra sanding with the coarse grit papers, it is all a process that will never be perfect every time with each piece of wood you turn.
Hope I did not bore you to tears with my long winded reply!
Merry Christmas,
Jeff
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