In Dutch there is the expression "Nee heb je, ja kan je krijgen." This roughly means that being told "no" after asking for something is only as bad as never asking in the first place.
Is there a more convenient English expression for this?
"There's no harm in asking" is a very common phrase
Also, perhaps when encouraging a timid person, "Go and ask, they can only say no".
Also, "Don't ask, don't get".
Expressions from sports that have passed into common usage (in AmE) include "you miss 100% of the shots you never take" and "you can't score if you don't shoot", the latter perhaps being open to misinterpretation in the context of romantic relationships.
'If you don't ask you don't get' is in pretty common usage with many minor variations.
There's a colloquial alternative from north east england, which I'm quite fond of:
'Shy bairns get nowt.'
This sounds very much like the saying no such thing as a stupid question.
To quote at a bit of length from its Wikipedia article (because it's worth it):
"(There's) no such thing as a stupid question" is a popular phrase with a long history. It suggests that the quest for knowledge includes failure, and that just because one person may know less than others they should not be afraid to ask rather than pretend they already know. In many cases multiple people may not know but are too afraid to ask the "stupid question"; the one who asks the question may in fact be doing a service to those around them . . .
Carl Sagan, in his work The Demon-Haunted World: Science as a Candle in the Dark said: "There are naive questions, tedious questions, ill-phrased questions, questions put after inadequate self-criticism. But every question is a cry to understand the world. There is no such thing as a dumb question".
A woman, recounting a story about an old man who used to answer all her "stupid questions", explained "Chica, if you ask a question it makes you look stupid for 5 minutes – but if you don't ask – you stay stupid for fifty years, so always ask questions in your life".
A 1970 Dear Abby column in The Milwaukee Sentinel said: "There is no such thing as a stupid question if it's sincere. Better to ask and risk appearing stupid than to continue on your ignorant way and make a stupid mistake."
Colin Powell says: "there is no such thing as a stupid question, only stupid answers". Presentation Skills That Will Take You to the Top says that within the business world, the adage holds true. The book adds "a question might be uninformed, tangential, or seemingly irrelevant, but, whether the presenter perceives it to be stupid or not, every audience member has every right to ask any sort of question".
In the Line of Fire: How to Handle Tough Questions – When It Counts suggests that there are no stupid questions, rather there are tangential questions, and that these should be dealt with swiftly and effectively.
Designing Field Studies for Biodiversity Conservation says "there's no such thing as a stupid question, as long as it ends in a question mark".
Obviously, it's been used in mostly different contexts in each of these, but the essential part of the statement remains the same.