Affirmanti, non neganti, incumbit probatio

AFFIRMANTI, NON NEGANTI, INCUMBIT PROBATIO
a more common form: Ei incumbit probatio qui dicit, non qui negat

Meaning: The proof lies upon one who affirms, not upon one who denies.

The maxim provides a rule in establishing a presumption of who initially carries the burden of proof. This is a deep-rooted and well known maxim, mentioned in the Blackstone's Commentaries (Book 3, p.366 (1791)) as one established both in common and civil laws. It appears to be a part of the Justinian I's Corpus Juris Civilis (Digest book*), completed in 533 A.D. And even there, it is referred as "A maxim of Paulus," enforced by the Emperor Pius' rescript. Its full cite and a detailed account are given here.

De Minimis Non Curat Lex

DE MINIMIS NON CURAT LEX

Meaning: The law cares not for trifles.

This maxim may be seen as one of the principles of judicial economy―that the court should not spend its time on trifling matters, or that some trifling details should not divert court's decision on a material point.

How rare an accident may still be "foreseeable"? 1 in 641,025 years.

In a recent strict liability case, Collins v. Navistar, 214 Cal.App.4th 1486 (2013), court held that it is possible for a vehicle manufacturer to foresee an event, with an effective chance of .003―.009 per billion vehicle-miles.

Allegata Et Probata

ALLEGATA ET PROBATA 

Meaning: The things alleged must agree with the things proved.

This rule applies to the proofs presented at trial, holding that such proofs have to be corresponding with what was alleged in the pleadings. Proving a fact not alleged is disallowed as a "variance."
The rule believed to be applied strictly in the Medieval period, but got relaxed in more recent times, so that the presented proofs need only to relate to the allegations. Variances to some immaterial degree become allowed.