To have an image of bamboo in one's mind
To be prepared; to have a plan in advance
Positive
我虽然还小，可是对要从事的职业已胸有成竹了 | Wǒ suīrán hái xiǎo, kěshì duì yào cóngshì de zhíyè yǐ xiōngyǒuchéngzhú le
I'm still young, but I already know what I want to do for a career
[Source]
你是担心无法通过期末考试，还是胸有成竹呢？ | Nǐ shì dānxīn wúfǎ tōngguò qímò kǎoshì, háishì xiōngyǒuchéngzhú ne?
Are you worried about passing the final exam, or are you prepared?
[Source]
None
成竹在胸 (chéng zhú zài xiōng)
The famous scholar in the story, 文同 (Wén Tóng), was also known as 与可 (Yǔ Kě). This is the same 与可 that appears in the title of the work from which this chengyu originated.
《文与可画筼筜谷偃竹记》(Wén Yǔ Kě Huà Yún Dāng Gǔ Yǎn Zhú Jì) by 苏轼 (Sū Shì), a great writer and calligrapher from the Northern Sòng Dynasty (宋, 960-1127)
In the Sòng Dynasty (宋, 960 - 1279), there was a famous scholar named 文同 (Wén Tóng). 文同 loved to paint pictures of bamboo, and the pieces he produced were so incredibly lifelike that people would come from all over to commission his work.
The reason that 文同 excelled at painting bamboo was that he had spent years extensively studying it. He often went for long walks in bamboo forests, and he had also planted bamboo in the front and the back of his house. Regardless of the weather or the season, he would frequently go out and study the plants' length, leaf size, and appearance in sunlight, rain, and wind. After many years of doing this, he knew what bamboo looked like in every possible situation, and so he could confidently draw lifelike bamboo whenever he wanted or needed to.
Once, a friend and poet named 晁补之 (Cháo Bǔ Zhī) stopped by 文同's house. He studied the paintings of bamboo for a long while and became so impressed that he wrote a poem of praise. "胸有成竹" was a line in that poem.