Making nitroglycerin requires fairly strict temperature control while running the reaction. Ignoring this aspect is a common rookie mistake. If it gets too warm

Making nitroglycerin requires fairly strict temperature control while running the reaction. Ignoring this aspect is a common rookie mistake. If it gets too warm, the nitric acid will essentially auto-catalyze its own decomposition (the brown fumes), which is never pleasant and ruins the reaction. Being too aggressive with the cooling has other issues. I think amateurs underestimate the importance of temperature control when trying to synthesize chemicals. There is a lot more too it than mixing ingredients like a cocktail.