There's tasks where experience doesn't tell you ahead of time how long something takes. If you need to figure out a [novel take on an] algorithm, it'll be hard

There's tasks where experience doesn't tell you ahead of time how long something takes. If you need to figure out a [novel take on an] algorithm, it'll be hard to predict the time even if you did things like that plenty times before. And you'll be able to judge the remaining work after pretty decently.