I'd agree Partypooper,1/1 about a 4/5 is incredible odds, but only in hindsight after the race of course.Unaccountable variables assures that 1/1 is never a sane bet or you must embrace "any price a winner" logic [Your other name must be wind-up]
I think stats show one in four favorites win all races.ANY odds you accept below 4/1 puts your pot at risk statistically [only]. We can accept below this often because of known variables that can genuinely alter the stats,but even 2/1 in my opinion cannot allow for unknown variables,especialy personal error.You cannot be sure that your 4/5 judgement is correct before the race,can you? .Obviosly not or alternatively,you have become extreamely wealthy from your very astute judgements.

At what point odds become a no bet is a personal assesment of where we indevidualy set the unknown. For me it's 3/1 and I'd probably be better off at 4/1 as I'm sure most of us overestimate our ability.