Sometimes there are dubious dynamics in the printed parts. For instance, in the last movement of Beethoven’s 5th. Symphony there is a solo passage for cellos and basses with an accompaniment of the upper strings playing chords on the off beat. I remember de Sabata asking the upper strings to lower their fortissimo so as to let the cellos and basses be heard above the din.
In the Variations in Schubert’s “Trout Quintet” one variation is the Theme played by the cello and bass. The piano part is marked F or FF and invariably the pianist thumps it out drowning the cello & bass.
Sometimes the cello and bass part needs to be played really strongly, for instance in the opening of Mendelssohn’s “Elijah”.
Opera and Ballet often need the principal bass to play up so as to set the tempo in the first bar or two of a piece such as Bertha’s aria in the last act of Rossini’s opera the “Barber of Seville”, or in the allegro in the first act of Verdi’s “La Traviata” after the first couple of bars intro.
It is only after much experience as a player that you can judge whether or not to decrease or increase the sound to make the bass part more viable. Usually an experienced conductor will tell you. There was a bass player who, when playing the” Messiah” put some very sticky resin on his bow and then declared to the conductor, “Now I’ll show you ‘Who is the King of Glory! ‘” Don’t make the mistake of trying to lead the orchestra: I can quote a conductor’s remark to Dragonetti. “Please, Signor Dragonetti, let me have my Orchestra back!”