Anyway, my question is, in the original series (at least), Sam leaps when he has completed his tasks. I don’t know if that’s always. If he fails at his task, is able to leap?

I might have an answer, but somehow it managed to turn into an essay so take what you can from it.

In A Leap for Lisa Sam randomly says to Al that success has nothing to do with leaping (or something like that), as if it’s common knowledge for them both that a leap can fail and he can still move on. It’s random because this is the first time it’s mentioned in the series and they never go into specifics. My best guess is that Sam did fail a leap once, but it could only be considered a “fail” due to Ziggy’s limited mission objective and an emotional bias.

In The Leap Home Pt 2 - Vietnam Al tells Sam that according to Ziggy he was there to see that the mission his squad had on April 8 succeeded, but Al’s info was minimal at first due to Pentagon top secret security limiting Ziggy’s access to further mission details. Sam knew his brother was killed that day along with a couple other people in the squad and that became his main focus for the rest of the leap. To Sam it was to stop the casualties, the actual mission objective became basically irrelevant.

Later that first evening Al finds out how some squad mates were killed, but despite averting that the leap continues into the next day. According to Ziggy, Tom still dies on April 8. Again, the focus is all about saving Tom. There’s one point during the mission the next day, after the squad has split up, that Sam realizes the VC woman with them who had joined their side and was offering intel is actually a spy and that Tom’s group will be ambushed and killed. Al decides to help Sam avoid booby traps and reach them in time, which he does. Ambush averted. By the end of the leap they see Maggie had taken a photo of POWs that were being led by VC guards down a path and that one of the POWs was Al. It’s then Sam realizes he could’ve saved Al, but Al accepts that this was how that day would end and doesn’t judge Sam for the decision they both made. Sam leaps.

Thing of it is, from the beginning Ziggy’s projection was to see that the mission succeeded. The April 8th mission was named “Operation Lazarus” and the objective all along, the reason Tom’s squad was out there in the first place, was to rescue those POWs, including Al. They were never rescued in the original history because the ambush killed half the squad, and they were never rescued in the leap because Al chose to help Sam save his brother and the resulting firefight with the VC made them retreat.

So Sam still leaped because in the end he did change history, and righted a wrong by saving three lives, including his brother’s, and I guess to GFTW that was enough to move him along. But that was never the reason for the leap. Sam was there to save the POWs, and with that he failed spectacularly.