Type 1 for nearly sixty years.
This is a huge problem with diabetes. Whenever anything goes wrong according to the diabetic rules we are given as gospel, we are told it is stress or undeveloped infection or something. We diabetics always feel we are being blamed because we know our own disease very well, and the reasons doctors and nurses give always feel like a cop out, an inadequate excuse for the doctors not having an accurate view of what we know and what we go through.
The truth is probably in between. It is a stinking, horrible, difficult, changeable disease. Some doctors and nurses are beginning to give up pretending that they know everything (meaning it is always our fault) and acknowledge that it is a nightmare disease which is different for each person, often different every day.
I have found my diabetes marginally more stable using a pump and sensors, but it still behaves irrationally. With precisely the same regime of food, exercise, insulin and stress, the BG results can be completely different. Very occasionally with very high (18-22) BGs that won't come down despite large extra boluses. My BG suddenly starts falling very fast 6 hours after the last bolus. Insulin is only supposed to last 2-3 hours, How is this possible? Many of the previous contributions give examples which also don't follow the rules.
Keep cool. Keep notes. Try and work out things for yourself. Things change. This weeks nightmare results will probably be different next week. I try to be sensitive to my diabetes and be intuitive. I take more insulin for breakfast if I feel like there will be a BG spike in the hours following. Sometimes it works, sometimes my frequent BG testing saves me from problems. I haven't had hospital treatment for a hypo for 40 years in spite of low hypo awareness, because I'm careful and test frequently and I still can see, have all my limbs and garden three allotments at 75.