這些都是過去同學看了別人的書來問我的題目：
杜邦公式、現金轉換循環 (註1)、自由現金流量、技術分析、景氣對策訊號燈、現金殖利率、股債蹺蹺板、covered call、naked put (註2)、ROA，
通通都是錯的。
These are some of the questions that students asked me after reading other books: DuPont formula, cash conversion cycle (Note 1), free cash flow, technical analysis, prosperity countermeasure signal light, cash yield, stock and debt seesaw, covered call, naked put (Note 2), and ROA. However, they are all incorrect.
註1:
現金轉換循環 (Cash Conversion Cycle，CCC)
= 銷貨天數 + 應收帳款收現天數 – 應付帳款付款天數
天數越短的公司，表示其營運效率越高。一樣，這又是一個無用的指標：
1. 作假帳的公司CCC反而會下降
作假帳的公司，把貨出到人頭公司，卻沒錢收回來
CCC = 把貨賣出去的天數下降 + 把錢收進來的天數上升 - 付錢給上游的天數上升 = 下降
2. 博達正是一家CCC下降的公司
它的存貨下降、應收也降，現金增加，卻都是假的
3. 不知循環天數長到多少才會出事 ?
4. 不給客戶賒帳，常常是做不到生意的
Note 1:
Cash Conversion Cycle (CCC)
= Days Inventory Outstanding + Days Sales Outstanding – Days Payable Outstanding
In theory, the shorter the cycle, the higher a company’s operating efficiency. In practice, however, the CCC can be a misleading or even useless indicator:
1. For companies manipulating their books, the CCC may actually improve. They record shipments to shell companies without ever collecting the cash.
CCC = Fewer days to “sell” goods ↓ + Longer days to collect cash ↑ – Longer days to pay suppliers ↑ = Net decrease.
2. Procomp (2398) was a classic example. Its inventory declined, receivables fell, and cash balances rose — but all of it was fabricated.
3. No one can predict at what point an extended cycle will trigger a collapse.
4. Extending credit is often unavoidable. In many industries, especially electronics, refusing to grant credit terms means losing business altogether.
註2：
選擇權策略
covered call ：持有現股+賣出call
naked put ：想買股票的同時賣出put
這兩者在實用上有很大問題
一是covered call 用於回檔或橫盤；
naked put 用於上漲，可是如何知道股價接下來會回檔或上漲 ?
二會因小失大
covered call：持有現股+賣出call。
1,300元的宏達電貴了理應賣掉，
卻因這個賣出call而不敢賣，以免call被執行時無股票可給，從此股價江河日下，一去不復還。
因貪圖1元權利金，痛失賣股良機。
若是仍然便宜的好股票，未來仍有可觀的上漲空間，為多賺一點點權利金，而冒著被迫提早賣掉現股的危險。
naked put：想買股票的同時賣出put。中碳跌到便宜價80元，賣出put，80元的中碳是難得買點，卻因賣出put而不敢買，以免put被執行時沒錢可買，從此中碳股價一路上漲，因貪圖1元權利金，失去賺好幾倍的機會。
Note2:
Option Strategies
Covered Call: Hold the stock + sell a call
Naked Put: Intend to buy the stock while selling a put
Both strategies face serious practical challenges:
1. Uncertainty about market direction. A covered call is best suited for a pullback or sideways market. A naked put works better in a rising market. But in reality, no one can predict with confidence whether the stock will pull back or rally.
2. Small gains, big risks
Covered Call: HTC(2498) at NT$1,300 was clearly overpriced and should have been sold. Yet the investor, having written calls, hesitated to sell the shares for fear of being unable to deliver if assigned. The stock then collapsed and never recovered. For the sake of just NT$1 in premium, they missed the chance to exit at the peak.
Even with undervalued, high-quality stocks, selling calls for a small premium carries the risk of being forced to sell too early, sacrificing significant future upside.
Naked Put: China Steel Chemical Co.(1723) fell to NT$80, a rare bargain price. Selling a put at that level looked appealing. But since NT$80 was itself a great entry point, the investor held back, worried about lacking the cash to cover assignment. The stock then went on a strong rally. Once again, chasing a NT$1 premium cost them the opportunity to earn many times that amount.