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To calculate how long the Mariners have been disappointing fans, I think we should go back to when the 2002 season tanked. On August 15, 2002, the Mariners were 27 games over .500 and in first place. On August 22, 2002, the Mariners fell out of first place for good. I'm not sure when the disappointment started, but it was some time that week.
So, from August 15, 2002 to today, we have 5646 days of disappointment in the Mariners.
From August 22, 2002 to today we have 5639 days of disappointment. I think we should be charitable and give the Mariners the extra week of non disappointment. We didn't think the Mariners could lose back then, so disappointment was probably a delayed onset.