I feel like the more days pass the less belief I have that I can carry on the streak. I’m so used to failing that it’s like I’ve lost the belief I can succeed.
At least two things are happening: 1) You're 'white-knuckling' through, meaning that you're not entirely committed, and so each day the resolve becomes less and less; and 2) You're already feeding or responding to the urges toward acting out.
It's very challenging to keep resolve or will-power going, and that alone isn't what helps us. That's why habit change is so important, and mindfulness.
About the length of time, instead of looking too far ahead, do it day by day. Like say, "I made it yesterday, I'll make it today." Or, I've made it for 6 days, I can do another day, and another..." so on.
My urges also aren’t helped by the fact that sometimes I go to NSFW Twitter pages before clicking away from them. So it’s like I’m toying with the idea before deciding against it. Eventually if I do that enough times I will relapse though.
We definitely have to give ourselves a fighting chance. I know p-subs have been a particular struggle of mine, but if I didn't address this, I would just continue setting myself up for failure. Also, if we can say 'No' to the pitfalls on social media, we can say 'No' when we're tempted toward actual PMO.
Address the smaller snakes, and the bigger dragons will fall.