Learn German: Das Experiment misslingt, da wir nicht aufpassen. - The experiment fails since we do not pay attention.

The prefix miss- is inseparable. It often adds a negative meaning or indicates failure, much like 'mis-' in English. Because it is inseparable, it always stays attached to the verb in the present tense, unlike separable prefixes.

Is misslingen related to another common German verb?

Yes, it is the direct opposite of gelingen (to succeed). The miss- prefix replaces the ge- prefix to create the negative meaning. Both verbs are very common and behave similarly, often taking a dative object (like Es misslingt mir for 'I fail at it'), though here it just describes the experiment directly.

Why is the separable verb aufpassen written as one connected word at the end?

The word da (since/because) introduces a subordinate clause, which forces the conjugated verb to the very end of the sentence. When a separable verb is pushed to the end like this, its prefix (auf-) and the verb stem (passen) recombine into a single word.

Could I use weil instead of da in this sentence?

Yes, weil and da mean the same thing and both push the verb to the end of the clause. da is often used when the reason is considered known to the listener or as a slightly more formal alternative, similar to using 'since' instead of 'because' in English.